This invention relates to a thermal image recording apparatus (hereunder referred to as a "thermal recording apparatus") with which an image corresponding to image data is formed on a thermal recording material (hereunder referred to as a "thermal material") using a thermal head. This invention also relates to a thermal image recording method.
Thermal materials comprising a thermal recording layer on a paper or film substrate are commonly used to record images produced in diagnosis by ultrasonic scanning. This recording method, commonly referred to as thermal image recording, eliminates the need for wet processing and offers several advantages including convenience in handling. Hence, the use of the thermal image recording system is not limited to small-scale applications such as diagnosis by ultrasonic scanning and an extension to those areas of medical diagnoses such as CT, MRI and X-ray photography where large and high-quality images are required is under review.
As is well known, the thermal recording apparatus uses the thermal head having a glaze in which heat generating elements corresponding to the number of pixels of one line are arranged in one direction and, with the glaze a little pressed against the thermal recording layer of the thermal material, the thermal material is relatively moved in a direction approximately perpendicular to the direction in which the heat generating elements are arranged, and the respective heat generating elements of the glaze are heated in accordance with the image data to be recorded to heat the thermal recording layer, thereby accomplishing image reproduction.
When the thermal material is pressed under the heated thermal head, the heat-sensitive substances, the lubricant and other substances in the thermal recording layer are fused on the surface to permit image reproduction. Hence, with the continued image recording, stain and the fusion products of the lubricant and other substances in the thermal recording layer tend to accumulate on the surface of the thermal head and unevenly recorded images will occur if the excessive accumulation of the fusion products gets stuck between the thermal material and the thermal head.
In addition, the fusion products adhering to the surface of the thermal head will gradually increase in the strength of adhesion as they are kept heated with the thermal head and in some cases, they will stick so tenaciously that they cannot be easily removed by means of liquid detergent or other cleaning solutions. If the tenacious substances are difficult to remove by the cleaning operation, the only practical way to be adopted has been to scrape off the deposits from the surface of the thermal head by a suitable means such as a lapping film having a strong abrasive effect.
The lapping film has an abrasive such as alumina particles buried in the surface of a substrate film and the deposits adhering tenaciously to the surface of the thermal head can be scraped off by delivering this lapping film in place of the thermal material. However, the abrasive effect of the lapping film is so great as to remove the protective ceramic coating on the thermal head and, hence, the thermal head will wear prematurely before the end of its expected service life.
The lapping film has the advantage of being able to remove any tenacious stain and deposits but, on the other hand, the application of the lapping film is very noisy and, hence, is not suitable in hospitals.
As a further problem, the user has to perform periodic maintenance of the thermal recording apparatus, which is simply a waste of time.